Child abuse and neglect is the leading cause of trauma-related death in children < 4 years age, killing more children than motor vehicle crashes and drowning combined. Every year in the US, nearly 2,000 children die, 18,000 are permanently disabled, and 150,000 children are seriously injured from child abuse and neglect. Fractures are second only to bruising as a presentation of abuse and indicate the child is being subjected to trauma that is potentially life threatening. Humerus fractures are common in child abuse, especially children 1 year or less, but can also occur accidentally. Because caregivers fabricate histories as to how the injury occurred, and because children are too young or often afraid to communicate what happened, the clinician must decide if the reported accident history and injury are consistent and compatible. A current lack of biomechanical understanding of fractures in children makes differentiation between intentional and unintentional trauma more difficult. Decisions are typically empiric rather than evidence-based, resulting in both missed cases of abuse and over-diagnosis in innocent families. Because the child's safety may rest on this single determination, a more scientific approach is needed. Before one can better identify injuries resulting from child abuse, one must first gain a more scientific understanding of the injury mechanisms and the resulting forces necessary to generate fractures in the infant and child. The PIs have chosen to focus their study on those children 0-10 years who present with accidental humerus fractures. The study is designed to increase scientific knowledge of pediatric humerus bone strength through assessing bone geometry using plain x-rays and bone mineralization using dual energy x-ray absorptiometry (DXA). Additionally, for each case they intend to advance the biomechanical understanding of pediatric accidents through scene investigations coupled with biodynamic calculations characterizing the accident. By building a database of these case-based injury scenarios that are truly unintentional and well documented, the PIs can begin to better understand the relationship between intrinsic biological properties of bone, fracture incidence and extrinsic biomechanical characteristics of a specific injury scenario. The proposed comprehensive model, which focuses on the relationship between case-specific intrinsic biological properties and extrinsic biomechanical characteristics of the specific accident, is the first step towards aiding clinicians in objectively identifying false accident histories. Through the use of computer simulation techniques they will further the understanding of how accident environment factors can influence key biomechanical measures associated with injury risk. The project specific aims include: 1. Conduct a clinical study in young children with humerus fractures to explore the relationship between radiographic derived bone properties and biochemical measures. 2. Develop and validate computer simulation models to investigate the biomechanics of hypothetical common pediatric falls. The long term goal is to develop a clinical tool that predicts the likelihood of pediatric fracture for a given accident scenario aiding clinicians in determining between intentional and unintentional injury.